| Traditional songgao(TS)is made of glutinous rice powder and japonica rice powderand sugar.However,becuase of its limited nutrients and high energy,Songgao can not satisfy the request that people pay more attention to health.Therefore,in order to maintain the vitality of the traditional food and improve people's physical health.We shoulduse modern science and technology to remake the traditional foods and improve their quality.In this study,based on the TS production formula,we used purple sweet potato powder to replace japonica rice powder and optimized the production process of purple sweet potato Songgao(PSPS).Furthermore,we studied the physical and chemical properties during storage and shelf life of PSPS.Firstly,by using single factor and L9(34)orthogonal experiment,the effect of the amount of water,raw material powder ratio(glutinous rice powder,japonica rice powder and purple sweet potato powder)and Songgao steaming time on the quality of PSPS was studied.The PSPS preparation process parameters were optimized by ragarding sensory evaluation as target.The optimized parameters were as follows: the ratio of glutinous rice powder,japonica rice powder: purple sweet potato powder4:2:4,water content 50%(the total quality of the raw material powder),steamed time25 min.On the basis of the optimization for preparing PSPS,the changes of the physicochemical properties of the PSPS under different storage temperature,i.e.the room temperature(25?)and refrigeration temperature(4?)were studied.The fresh PSPS moisture content(40.3%)was higher than the traditional fresh Songgao(33.4%).With the increase of storage time,the water content and water binding capacity of PSPS gradually reduced,which was same with the varied tendency of TS.In the whole storage time,the moisture content of purple sweet potato is higher than TS,mainly due to the high fiber content in purple potatoes powder.For different storage temperature,the moisture content Songgao under 4? was higher than 25?,mainly because the low temperature reduced the evaporation of water.Texture profile analysis showed that with the increase of storage time,the hardness of PSPS and TS increased;but the increase extent of TS was higher compared to PSPS.When the storage time was more than 3 days,the hardness of the two types Songgao all declined,which was because the sponge had the crisp texture after water evaporated.Differential thermal analysis(DSC)result indicated that starch retrogradationdegree in the PSPS and TS gradually increased with the increase of storage time.Compared with the TS,the enthalpy of melting the amylopectin recrystallization was lower,suggested that starch retrogradation degree of starch in the PSPS was lower than TS.Compared with 25? storage conditions,the retrogradation degree of two types Songgao was higher than 4 ?,which confirmed that low temperature speed accelerated the starch aging.X-ray diffraction analysis of two kinds of Songgao samples storage at 4 ?showed when the storage time was 0d,the X-ray diffraction curve of PSPS and TS had four obvious characteristics diffraction peak at 15°,18°,17° and 23°,which belonged to the A-type X-ray diffraction pattern.The diffraction peak at 18° was strongest,while the diffraction peaks at 15° was weakest.The crystallinity of TS and PSPS starch was 6.5% and 4.1%,respectively.After the storage for 1 d,3 d and 7 d,the starch crystal structure changed into "V",which had a strongest diffraction characteristic peak at 19°.The crystallinity of starch in TS was higher than PSPS at the same storage time.In vitro digestion results showed that with the extension of storage time,the content of slow digestion starch and resistant starch of PSPS and TS gradually increased,while the fast digestion starch content reduced.Storage temperature had effect on the formation of fast and slow digestion starch in recrystallized starch,and4? was beneficial for the formation of resistant starch(p<0.01).To further study the effect of starch structure on the starch in vitro digestion characteristics in all powder,scanning electron microscope was operated for two types Songgao stored at 4? and25 ? for 3d.The observation analysis showed that purple sweet potato Songgao starch surface was smoother than the TS,and both had stratiform structure and broken fragments.Finally,we investigated the changes of total number of bacteria and mold during the storage time.The results showed that with the decrease of storage temperature,the total amount of bacteria and mold growth has slowed in the songgao sample,and the growth rate of PSPS than TS.The accelerated shelf life test method(ASLT)results showed that the security shelf life of the PSPS is 4 d at 25?,compared with the TS for prolong the storage period.The ASLT result showed the shelf life of PSPS is about5.656 d stored at 20? and humidity was 60%.The shelf life PSPS is about 16 d when stored at 4? and humidity is 60%. |
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